Yes I for sure do assume Lion dealt in good faith.
<<<< see mon
If Lion had cheated Unicorn, Altansarnai would surely have thought about it and/or Kamoko would have said it outright when they talked it over. Accusing Lion of dishonor on this account seems like malicious speculation. Meanwhile, Unicorn definitely, unarguably reneged on their word - this is clearly dishonorable behavior and only reinforces the Unicorn's barbaric reputation as well as angering Lion.
For Lion, the correct choice is what bushido demands. And in this instance, Unicorn has no ground to deny Lion recompense for Unicorn's dishonorable behavior. Even among barbarians, one can find some shame. Hence Shono's reaction to his mother's selfish whimsy.
Unicorn must now place its hope in Toturi's merciful nature.